1. Field of the Present Description
The present invention relates in general to the field of rotor hubs for aircraft. In particular, the present invention relates to a dual spring rate damper for soft in-plane rotor hubs.
2. Description of Related Art
Many aircraft rotors, especially those for helicopters and tiltrotor aircraft, include a lead/lag hinge designed to allow in-plane motion of a blade about an axis generally normal to the plane of rotation, such that the blade “runs in” or “gets behind” with respect to other blades. This is mainly to compensate for the extra rotational speed that comes with “blade flapping” and to compensate for differences in blade aerodynamic drag encountered at various moments of one rotational cycle.
To prevent excessive motion about the lead/lag hinge, dampers are normally incorporated in the design of this type of rotor system. The purpose of the dampers is to absorb the acceleration and deceleration of the rotor blades and maintain the frequency of the lead/lag motion within a desired range. Often, the damper is an elastomeric damper. Normally, the spring rate chosen for a lead/lag damper is a compromise between the value required for the desired in-plane stiffness and a value that reduces load and fatigue on the rotor and other aircraft components.